latex-pictures

 % This picture represents the behaviour of the morphisms of a projective system
 % (X_i, \phi_{i, j}
 % Copyright Pablo (C) 2021
 \begin{tikzpicture}[ampersand replacement=\&]
   % The objects
   \matrix(m)[matrix of math nodes,row sep=2em,column sep=2em,minimum width=2em]
   {     \& X_j \& \\
     X_i \&     \& X_k \\};
 
   % The arrows
   \draw[->] (m-2-3) -- node[below]{$\phi_{i k}$} (m-2-1);
   \draw[->] (m-1-2) -- node[above left]{$\phi_{i j}$} (m-2-1);
   \draw[->] (m-2-3) -- node[above right]{$\phi_{j k}$} (m-1-2);
 \end{tikzpicture}